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21.
Data collected from operating plants can be mined to extract information related to both normal and fault modes of operation. Correspondence analysis (CA), that decomposes a measure of row–column association, to generate the lower dimensional space has been recently proposed [1] for this task. CA represents the association between samples and variables in terms of angle based measures on a biplot. Thus, toward clearer resolution of the faults, polar clustering and classification procedures are necessary. In this paper, we develop a methodology to mine the operating data and build such clusters. We demonstrate the application of this methodology on data generated from simulations and experiments involving representative systems,for detecting parametric changes and resolving sensor and actuator biases. 相似文献
22.
Material properties and operating configurations of membrane reactors for propane dehydrogenation 下载免费PDF全文
Seung‐Won Choi Christopher W. Jones Sankar Nair David S. Sholl Jason S. Moore Yujun Liu Ravindra S. Dixit John G. Pendergast 《American Institute of Chemical Engineers》2015,61(3):922-935
A modeling‐based approach is presented to understand physically realistic and technologically interesting material properties and operating configurations of packed‐bed membrane reactors (PBMRs) for propane dehydrogenation (PDH). PBMRs composed of microporous or mesoporous membranes combined with a PDH catalyst are considered. The influence of reaction and membrane transport parameters, as well as operating parameters such as sweep flow and catalyst placement, are investigated to determine desired “operating windows” for isothermal and nonisothermal operation. Higher Damköhler (Da) and lower Péclet (Pe) numbers are generally helpful, but are much more beneficial with highly H2‐selective membranes rather than higher‐flux, lower‐selectivity membranes. H2‐selective membranes show a plateau region of conversion that can be overcome by a large sweep flow or countercurrent operation. The latter shows a complex trade‐off between kinetics and permeation, and is effective only in a limited window. H2‐selective PBMRs will greatly benefit from the fabrication of thin (~1 µm or less) membranes. © 2014 American Institute of Chemical Engineers AIChE J, 61: 922–935, 2015 相似文献
23.
Magnetic resonance image denoising using nonlocal maximum likelihood paradigm in DCT‐framework 下载免费PDF全文
P. Krishna Kumar P. Darshan Sheethal Kumar Rahul Ravindra Jeny Rajan Luca Saba Jasjit S. Suri 《International journal of imaging systems and technology》2015,25(3):256-264
The data acquired by magnetic resonance (MR) imaging system are inherently degraded by noise that has its origin in the thermal Brownian motion of electrons. Denoising can enhance the quality (by improving the SNR) of the acquired MR image, which is important for both visual analysis and other post processing operations. Recent works on maximum likelihood (ML) based denoising shows that ML methods are very effective in denoising MR images and has an edge over the other state‐of‐the‐art methods for MRI denoising. Among the ML based approaches, the Nonlocal maximum likelihood (NLML) method is commonly used. In the conventional NLML method, the samples for the ML estimation of the unknown true pixel are chosen in a nonlocal fashion based on the intensity similarity of the pixel neighborhoods. Euclidean distance is generally used to measure this similarity. It has been recently shown that computing similarity measure is more robust in discrete cosine transform (DCT) subspace, compared with Euclidean image subspace. Motivated by this observation, we integrated DCT into NLML to produce an improved MRI filtration process. Other than improving the SNR, the time complexity of the conventional NLML can also be significantly reduced through the proposed approach. On synthetic MR brain image, an average improvement of 5% in PSNR and 86%reduction in execution time is achieved with a search window size of 91 × 91 after incorporating the improvements in the existing NLML method. On an experimental kiwi fruit image an improvement of 10% in PSNR is achieved. We did experiments on both simulated and real data sets to validate and to demonstrate the effectiveness of the proposed method. © 2015 Wiley Periodicals, Inc. Int J Imaging Syst Technol, 25, 256–264, 2015 相似文献
24.
Girendra Pal Singh Pallavi Vishwas Madiwale Ramanand N Jagtap Ravindra V Adivarekar 《应用聚合物科学杂志》2014,131(19)
With growing environmental awareness, ecological concerns and new legislations, natural fiber‐reinforced plastic composites have received increasing attention during the recent decades. The natural fiber composites have many advantages over traditional glass fiber composites, including lower cost, lighter weight, environmental friendliness, and recyclability. This article reports the findings of the studies done on a new fiber, hitherto unexplored, extracted from Saccharum munja grass. The extracted fibers were further treated using sodium hydroxide to improve its performance in composites. Both treated and untreated fiber‐reinforced composites were prepared by hand lay‐up process using unsaturated polyester resin. Mechanical properties and thermal behavior of the composites were evaluated. The improvement in properties was found for alkali‐treated fiber composites. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40829. 相似文献
25.
Polyester (PET) nanocomposite fibers were spun by adding master batches of linear low‐density polyethylene (LLDPE) loaded with Montmorillonite (MMT) nanoclay after compatibilizing the PET and LLDPE. The spun fibers showed increased thermal stability as well as flame retardancy, which increased progressively with the amount of nanoclay loaded into the fiber. There is slight decrease in tensile strength of the fiber accompanied by decrease in elongation % indicating addition of nanoclay makes the filaments stiffer. The onset of crystallization temperature occurred at higher temperature in case of composite fibers than on the neat PET fiber because of nucleating effect of nanoclay. The dyeability of the fibers was not affected and also had very little impact on the flame retardancy of the fiber. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers 相似文献
26.
27.
Priyanka Singh Shailesh N. Sharma N. M. Ravindra 《JOM Journal of the Minerals, Metals and Materials Society》2010,62(6):15-24
An overview of the applications of porous silicon (PS) thin films, as antireflection coatings (ARC) in silicon solar cells
and transducers in biosensors, is presented. The reflectance spectra of PS films have been compared with other conventional
ARCs (such as SiNx TiO2/MgF2 and ZnS), and optimal PS ARC with minimum reflectance has been obtained. The implementation of PS into an industrially compatible
screen-printed (SP) solar cell by both the electrochemical etching (ECE) and chemical etching (CE) methods are reviewed. Porous
silicon films, formed via ECE for short anodization times, on textured n+ emitter ofc-Si solar cell having SP front and back contacts, lead to improvements in the performance of solar cells and demonstrate
their viability in industrial applications. 相似文献
28.
In the present work, we report the preparation of PLZT thin films in pure perovskite phase by RF magnetron sputtering without
external substrate heating and their integration with micro-cantilevers. The ‘lift-off’ process for patterning different layers
of a micro-cantilever including PLZT, Pt/Ti and Au/Cr was employed. The basic requirement of lift-off process is that the
deposition temperature should not exceed 200°C otherwise photoresist will burn out. Therefore, one of the aims of the present
work was to prepare PLZT film at lower deposition temperatures, which can be subsequently annealed to form pure perovskite
phase. This also strongly favours the incorporation of ‘lift-off’ process for patterning in the complete process flow. As
no external substrate heating was required in the deposition of PLZT film, this objective has been successfully accomplished
in the present work. The ‘lift-off’ process has been successfully adopted for patterning the composite layers of PLZT/Pt/Ti
and Au/Cr using thick positive photo-resist (STR-1045). Different types of cantilever beams incorporating PLZT films have
been successfully fabricated using ‘lift-off’ process and bulk micromachining technology. The proposed process can be advantageously
applied for the fabrication of various MEMS devices. 相似文献
29.
The relative activity of the potential slip systems in Sn is examined by comparing an experiment of a single shear lap deformation
with simulations using the viscoplastic self-consistent crystal plasticity model developed by Lebensohn and Tomé. In a single
shear lap specimen made using eutectic Sn-Ag solder on copper pull tabs, the initially polished side was characterized using
orientation mapping before and after 0.8 shear deformation at 25°C at a shear strain rate of 0.1/s. The critical resolved
shear stress of potential slip systems and the rate sensitivity was altered by trial and error until good agreement between
experimentally observed and computed texture was obtained. This result indicated that slip on {101) and {211) planes is much
more difficult to activate than on other slip systems for the grain orientations present in this sample. This particular sample
showed much activity on the {010)〈101] slip system, but the activation of this slip system may be related to the initial dominant
orientation in the specimen. This result is compared with literature and related experiments on ball grid arrays in a companion
paper in this volume that show similar trends. As lead-free solder joints are commonly single crystals or multicrystals, this
particular result is not indicative of lead-free solder joints as a whole, but must be interpreted in the context of a larger
data set. 相似文献
30.
A general expression for the pressure dependence of the energy gap of a series of group III–V and group II–VI ternary semiconductors have been derived based on Van Vechten’s dielectric theory. The results obtained are in good accord with the available experimental data. The trends in the variation of the pressure dependence of the energy gap with the nearest neighbor distance and Phillips ionicity are explored qualitatively. 相似文献